High perimeter stability burner

ABSTRACT

Herein a gas boiler burner ( 1 ) is described comprising a diffuser, suitable for diffusing premixed fuel gases in a combustion chamber, in which the diffuser comprises a diffuser central portion ( 10 ) and two diffuser longitudinally peripheral portions ( 5 ), the two diffuser longitudinally peripheral portions ( 5 ) being connected together through the- central diffuser portion ( 10 ), the central diffuser portion ( 10 ) extending longitudinally in a direction perpendicular to the flow of the fuel gases over a length l greater than zero and having transversal cross- sections shaped as a circumference arc having a uniform radius of curvature r, each of the diffuser longitudinally peripheral portions ( 5 ) being shaped as a portion of a sphere having radius r.

The present invention relates to a high perimeter stability burner for a gas boiler.

Gas boilers of the prior art comprise: a conduit for supplying a burner with a premixed gas-air mixture, a burner for the production of heat through the combustion of said mixture in a combustion chamber, and possibly a support element which may be connected to the heat exchanger and/or to the supply conduit to ensure the closure of the combustion chamber and/or for positioning the burner with respect to such combustion chamber.

The burner comprises a diffuser through which the premixed fuel and air gas which determines a flame pattern for the production of heat is conveyed. Usually the diffuser comprises a wall provided with a plurality of openings and having an inner surface fluidically connected with the supply conduit, and thus in contact with the unburnt mixture, and an outer surface whereon the combustion occurs.

Upstream of the diffuser (with reference to the direction of flow of the gas-air mixture) a distribution device, or distributor, may also be provided arranged on the side of the diffuser opposite to the combustion surface, usually comprising a wall with a plurality of through openings, configured so as to distribute the gas-air mixture in a substantially uniform manner or however in the desired manner towards the wall of the diffuser.

As it is well known, the heat produced by the combustion on the outer side of the wall of the diffuser is conveyed through the hot fuel gases to a heat exchanger for heating a fluid, for example water, which is subsequently conveyed to a user, for example to a heating system of an industrial process, residential environments or the like and/or domestic water.

Due to the specific needs of a controlled and differentiated heating it is essential to be able to vary the heating power of the burner.

It is possible to control the heating power of the burner through the variation of the flow rate of the fuel or of the mixture supplied to the diffuser. However, the width of the heating power range or the so-called modulation (ratio between maximum power and minimum power) of the burners of the prior art is limited. This is due to the fact that, when the fuel flow rate exceeds the optimal range which depends on the material, the specific area of passage (quotient between the passage area and the wall area) and the resistance of the diffuser to the mixture flow, problems related to instability of the flame occur which jeopardise the correct operation of the burner. In particular, upon increasing the heating power, the combustion area, and thus the flame, tends to move away from the diffuser with serious effects in terms of safety and emission of pollutant substances, such as carbon monoxide (CO).

Such phenomenon of the flame moving away from the diffuser is particularly relevant at the ends of the diffuser.

As a matter of facts, such ends are connected with the framework of the burner hence the temperature of the diffuser, in such areas, is inevitably lower than in the remaining areas.

In order to overcome this problem, the use of additional distributors in proximity of the diffuser or the use of diffusers suitably shaped by moulding is known. Both solutions are however complex in terms of manufacture and considerably affect the burner manufacturing costs.

Thus, the object of the present invention is to provide a burner capable of overcoming the aforementioned flame instability problems, and in particular the problem related to the flame detachment and which is simultaneously simple and inexpensive to produce.

This and other objects are attained by means of a gas boiler burner comprising a diffuser, suitable for diffusing premixed fuel gases in a combustion chamber, each cross-section of said diffuser having a uniform radius of curvature, wherein said diffuser comprises a diffuser central portion and two diffuser longitudinally peripheral portions, said two diffuser longitudinally peripheral portions being connected together through said diffuser central portion, said diffuser central portion extending longitudinally in a direction perpendicular to the fuel gas flow for a length l greater than zero and having a cross-section shaped as a circumference arc having a radius r, each of said diffuser longitudinally peripheral portions being shaped as a portion of sphere having radius r.

Such particular configuration of the diffuser allows attaining a flame stability also in case of increase of the heating power and also at the ends of the diffuser.

In particular, the aforementioned configuration allows obtaining a flow direction of the fuel gases exiting from the diffuser whose component in the direction perpendicular to the surface of the diffuser at the edges thereof is substantially null. Thus, it is possible to reduce the mixture flow at the edges and prevent the flame detachment phenomenon, also with high power modulations.

Herein the term “gas flow direction” is used to indicate the main direction of flow of the gases.

For the purpose of the present invention, the expression “the cross-section has a uniform radius of curvature” is used to indicate that each point of the cross-section has the same radius of curvature, i.e. it belongs to the same hypothetical circumference having such radius.

In order to better understand the invention and appreciate the advantages thereof, hereinafter a description of some exemplifying and non-limiting embodiments of the burner of the invention is provided, with reference to the attached figures, wherein:

FIG. 1 is a longitudinal sectional view of a boiler portion comprising a gas burner according to the present invention;

FIG. 2 is a perspective view of a gas boiler burner according to a first embodiment of the invention;

FIG. 3 is a perspective view of a gas boiler burner according to an embodiment of the invention, mounted on a framework;

FIG. 4 is a side view of the burner of FIG. 3;

FIG. 5 is the view along the cross-section B-B of the burner of FIG. 4; and

FIGS. 6 a-6 c show the vectorial breakdown of some flow lines of the fuel gases along the section of FIG. 5.

With reference to FIGS. 1-6, a gas boiler burner, is wholly indicated with reference number 1.

In particular, reference 1 indicates a burner which produces heat through the combustion of a premixed fuel gas, generally comprising fuel gas and air. Preferably, such fuel gases are completely premixed, i.e. no further component is added to the mixture supplied to the burner.

The burner 1 comprises a diffuser 2, which is suitable for diffusing fuel gases in a combustion chamber 3 (indicated with a dotted line in FIG. 1).

The burner 1 is mounted on a framework 9. The latter may be connected to the combustion chamber 3 through connection portions.

The framework 9 further delimits an opening for the passage of the fuel and air mixture.

The diffuser 2 includes a wall provided with a plurality of openings whose inner surface is fluidically connected with the gas supply conduit. The combustion occurs on the outer surface of such wall.

The diffuser 2 may comprise a distributor 4 of the known type, suitable for distributing the mixture to the diffuser 2 and arranged on the side of the diffuser 2 opposite to the combustion chamber 3.

FIG. 1 also shows a schematic representation of a heat exchanger 6 in contact with the combustion chamber 3, which is suitable for receiving the heat produced by the combustion on the outer side of the wall of the diffuser 2.

As shown in FIG. 2, three main directions have been identified: a longitudinal direction α, a transverse direction β and a radial direction γ. The longitudinal direction a and the transverse direction are orthogonal to each other and they are both orthogonal to the direction of flow of the gases entering into the burner 1, which is indicated in the figures with the arrows 7.

According to the present invention, each cross-section of said diffuser 2 has a uniform radius of curvature. In other words, each section obtained intersecting the diffuser 2 with a plane parallel to the plane B-B of FIG. 4 has a single radius of curvature, i.e. each point of the section belongs to an ideal circumference having such radius of curvature.

According to the present invention, the diffuser comprises a diffuser central portion 10 and two diffuser longitudinally peripheral portions 5, in which said two diffuser longitudinally peripheral portions 5 are connected to each other by said diffuser central portion 10. The diffuser central portion 10 extends longitudinally in a direction perpendicular to the flow of the fuel gases, i.e. in the longitudinal direction α, over a length l greater than zero. Furthermore the diffuser central portion 10 has a cross-section shaped as a circumference arc having a radius r, as shown in FIG. 5.

In particular as shown in such figure, the cross-section is preferably a semi-circumference.

Therefore, the diffuser central portion 10, extends transversely over a length equivalent to 2r.

Each of said diffuser longitudinally peripheral portions 5 is shaped as a portion of sphere having radius r, as shown in FIG. 4.

In particular, as shown in such figure, each of said portions is shaped as a quarter of sphere.

In other words, the radius of the spherical portion which forms each peripheral longitudinal portion of the diffuser 5 has a length equivalent to the radius of the cross-section of the central diffuser portion 10.

According to the preferred embodiment shown in the figures, the burner 1 also comprises a distributor associated to the diffuser 2 and suitable for distributing the fuel gases on the diffuser 2, which has a configuration substantially equivalent to the configuration of the diffuser 2. This is particularly observable in FIG. 5.

Said distributor 4 comprises a sheet provided with openings or a metal mesh or a porous material.

The diffuser 2, instead, comprises a mesh made of metal or ceramic fibres or a compact material having openings or a porous material.

According to preferred embodiments, the diffuser is connected to a framework 9 which is arranged substantially perpendicular to the direction of flow of the fuel gases entering the burner 1, indicated by the arrows 7.

In FIGS. 6 a-6 c, the arrow indicated with the reference number 7′ shows the direction of flow of the gases exiting from the burner 1.

As observable from such figures, the nearer to the ends of the cross-section the more the normal component on the diffuser 2 of the direction of flow of the gases exiting from the burner 1 decreases.

Therefore, such normal component will be minimum at the edges and maximum at the vertex of the circumference arc which constitutes the section.

Such phenomenon compensates the temperature drop typical of the ends for connection to the framework 9, thus avoiding the flame detachment in such critical areas.

The situation is analogous at the longitudinal section of the diffuser 2 in that each longitudinally peripheral portion of the diffuser 5 is shaped as a circumference arc having a radius r, thus the edges of the longitudinal section of the diffuser 2 have the same characteristics of the edges of the cross-section of the diffuser 2.

In other words, the nearer to the ends of the longitudinal section the more the normal component on the diffuser 2 of the direction of flow of the gases exiting from the burner 1 decreases.

Therefore, such normal component will be minimum at the edges and then gradually increase up to reaching a maximum at the entire length l of the diffuser central portion 10.

Hence, the normal component of the direction of flow of the exiting gases is minimum along all the perimeter edges of the diffuser 2 and thus the flame detachment phenomenon, critical in such areas, is controlled.

Therefore, such configuration of the burner 1, allows obtaining a flame stability also in case of increase of the heating power and simultaneously a burner that is simple and inexpensive to produce.

Within the description above and in the subsequent claims, all the numerical values indicating amounts, parameters, percentages, and so on and so forth shall be deemed preceded under any circumstances by the term “about” unless otherwise indicated. Furthermore, all numerical value intervals include all possible combinations of the maximum and minimum numerical values and all possible intermediate intervals, besides those specifically indicated in the text.

The gas boiler burner according to the present invention may be subjected, by a man skilled in the art, with the aim of meeting contingent and specific requirements, to further modifications and variants all falling within scope of protection of the invention. 

What is claimed is:
 1. Burner for gas boiler comprising a diffuser, suitable for diffusing premixed fuel gases in a combustion chamber, each cross-section of said diffuser having a uniform radius of curvature, wherein said diffuser comprises a diffuser central portion and two diffuser longitudinally peripheral portions, said two diffuser longitudinally peripheral portions being connected together through said diffuser central portion, said diffuser central portion longitudinally extending in a direction perpendicular to the fuel gas flow for a length l greater than zero and having a cross-section being shaped as a circumference arc having a radius r, each of said diffuser longitudinally peripheral portions being shaped as a portion of sphere having radius r.
 2. Burner according to claim 1, further comprising a distributor, associated to the diffuser suitable for distributing fuel gases on the diffuser, having a shape substantially equal to that of the diffuser.
 3. Burner according to claim 2, wherein said distributor comprises a metal sheet provided with openings or a metal net or a porous material.
 4. Burner according to claim 1, wherein said diffuser comprises a mesh made of metal or ceramic fibres or of a compact material having openings or a porous material.
 5. Burner according to claim 1, wherein the diffuser is connected to a frame substantially perpendicular to the flow direction of the fuel gas. 